[2] During the First World War, Mary Dalzell went to France as an ambulance driver in the First Aid Nursing Yeomanry, from October 1918 to June 1919.
[3] In 1939 she was promoted to the senior commandant, based in London; she was transferred later that year to the Women's Auxiliary Air Force (WAAF).
[2] She served as inspector-general from 1942 and succeeded Katherine Jane Trefusis-Forbes[4] to become the second Director of the WAAF, from October 1943[5] to November 1946.
[6] In this work, she toured WAAF locations abroad, including Belgium, Italy, and India.
[7] Mary Dalzell married William Lawrie Welsh, an officer in the Royal Air Force, in 1922.